AU721243B2

AU721243B2 - Drive for a plurality of transfer cylinders in a printing machine

Info

Publication number: AU721243B2
Application number: AU74125/96A
Authority: AU
Inventors: Anton Rodi
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Individual
Priority date: 1995-12-04
Filing date: 1996-12-04
Publication date: 2000-06-29
Anticipated expiration: 2016-12-04
Also published as: DE59605036D1; US5809883A; AU7412596A; EP0778128B1; EP0778128A1; JPH09174803A; DE19545114A1

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Heidelberger Druckmaschinen Aktiengesellschaft Actual Inventor(s): Anton Rodi Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: DRIVE FOR A PLURALITY OF TRANSFER CYLINDERS IN A PRINTING

MACHINE

Our Ref 473719 POF Code: 1386/1386 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- Drive for a plurality of transfer cylinders in a printing machine The invention relates to a device driving a plurality of transfer cylinders in a digital printing machine.

With conventional offset printing machines the transfer cylinders such as plate cylinder and blanket cylinder are connected to each other via gearwheels in order to be driven in synchronism. An absolute forced synchronization of the transfer cylinders via gearwheels is necessary to precisely maintain their relative phase position even after an arbitrary number of rotations.

In addition, bearer rings are provided at both ends of plate cylinder and blanket cylinder, said bearer rings are made of hardened and polished steel the respective outer dimension of which corresponds basically to the diameter of the pitch circle of the gearwheel of the respective cylinder. Together with the cylinders said bearer rings roll off against each other under a pre-load, which brings about a quietness of operation, protects the drive, and extends the service life of the printing plate.

It is the object of the invention to provide a drive for the transfer cylinders of a digital printing machine, the setup of said drive being particularly simple.

20 According to the invention there is provided a device for driving a plurality of transfer cylinders of a digital printing machine, comprising a motor to which one of the plurality of transfer cylinders is connected, and bearer rings rollable on one another under a preloading, the plurality of transfer cylinders being connected to one another via said bearer rings, and said transfer cylinders 25 which are not connected to the motor being substantially exclusively driven through said respective bearer ring.

:p pa p W:\chdisnodelete\74125-96.doc A digital printing machine operates, for example, as follows: a printing image is applied onto a first transfer cylinder which, for print-technical reasons, features a hardened surface, from said first transfer cylinder it is then transferred onto a second transfer cylinder having an outer cylindrical surface made of elastic material, from said second transfer cylinder it is transferred onto a substratums, with said elastic material being able to fit snugly to a substratum such as paper, for example, for the purpose of a uniform ink transfer. The first transfer cylinder corresponds to the plate cylinder of an offset printing machine, and the second transfer cylinder corresponds to the blanket cylinder of an offset printing machine.

9 -3- The invention does without any gearing elements provided between the transfer cylinders of the digital printing machine; the transfer cylinders are connected to each other merely via bearer rings which are generally disposed at the ends of the transfer cylinders. One of said transfer cylinders is driven by a motor of the printing machine and entrains the other transfer cylinder by means of the bearer rings. Due to the multiple torques required the driven transfer cylinder is preferably the one transferring the printing ink onto the substratum.

The invention takes advantage of the fact that a digital printing machine can dispense with an absolute synchronization between the transfer cylinders. A relative synchronization is sufficient i.e. the phase displacement along the transfer path of the printing ink is at least not greater than the desired print resolution due to the inevitable slip of the bearer rings. As a digital printing machine does not use a printing plate having the structure of the image to be printed, a complete printing image is rather produced with each machine stroke, the slight phase 15 displacements which add up in the course of time have no influence on the print result. This is also true in the case of driving not only the transfer cylinders of one printing unit but rather the transfer cylinders of a plurality of printing units in the manner described by the invention.

A prerequisite for such a relative synchronization is however that the pre- 20 load between the bearer rings of two transfer cylinders rolling off against each other is great enough for an entraining effect being produced by the friction of the bearer rings and not by the friction between the transfer cylinders. It is possible to manufacture bearer rings having a precisely defined diameter, whereas the rolling-off behaviour of the transfer cylinder are generally complicated, especially if one of said transfer cylinders is a cylinder having an outer cylindrical surface made of elastic material such as rubber, for example.

During machine operation blanket jams in front of a transfer location at which it is pressed against another transfer cylinder, for example. As a result thereof, the effective circumference of the blanket and its circumferential speed is increased by approximately 2 to 3 percent. If, according to the invention, transfer cylinders, one of them being a blanket cylinder, are driven via bearer rings, an appropriate selection of the diameter ratio of the bearer rings may, however, -4ensure that the circumferential speeds of the transfer cylinders are almost identical so that there is as little slip as possible at the transfer location.

Furthermore, it is to be taken into account that the coefficient of static friction between rubber and steel is approximately five times as great than that between steel and steel. If one of the transfer cylinders is a rubber cylinder, an inventive drive has to ensure that the contact force between the bearer rings is at least five times as great as the force with which the transfer cylinders are pressed against each other, as a rule it is even much greater in order to provide reserves for changing operating conditions. Moreover, the bearings of the transfer cylinders have to be designed so as to be able to absorb these forces.

On the other hand, the invention dispenses with any gearing elements between the individual transfer cylinders so that, compared with conventional printing machines, the drive is much simpler with respect to its setup and to a i large extent it is maintenance-free. The bearer rings ensure an extremely uniform 9 15 operation of the transfer cylinders which is not affected by any impact between any gearing elements.

The invention is suitable not only for systems having two transfer cylinders, as mentioned above, but also for a joint drive of three or more transfer cylinders.

In the case of, for example, three transfer cylinders of a printing unit connected to 20 each other in line, the middle transfer cylinder may be driven, whereas the other two are entrained via bearer rings. The transfer cylinders of several printing units disposed in line may also be connected to each other via bearer rings, with only e one of said transfer cylinders being driven. Even in the case of connecting several bearer rings in line, the slip at the bearer rings is small enough to ensure that the accuracy of the synchronisation is in a tolerable range.

Further features and advantages of the invention result from the description of several specimen embodiments and the drawing referred to.

Fig. 1 is a partially schematic side elevational view of a digital printing unit having two transfer cylinders; Fig. 2 is a sectional view taken along a line II II of the printing unit of Fig.

1; and Fig. 3 is a partially schematic side elevational view of a digital printing machine having transfer cylinders of a plurality of printing units, said transfer cylinders being connected to each other via bearer rings.

The digital printing unit shown in Figs. 1 and 2 comprises a first transfer cylinder 1 and a second transfer cylinder 2 disposed parallel to each other, with their circumferences contacting each other. The transfer cylinders 1, 2 are pivotmounted on side walls (not shown) of a printing machine. An imaging head 3 and an inking unit 4 extending over the entire printing width are provided at the circumference of the first transfer cylinder 1 The second transfer cylinder 2 features a drive shaft 5 connected to a motor 6. The figures show said motor 6 on an axis of the second transfer cylinder 2; however, said motor may, of course, also be disposed in the printing machine at any other location thereof and may be connected to the drive shaft 5 via power-transmitting elements such as a gearing, for example. Furthermore, the second transfer cylinder 2 features an outer cylindrical surface (not explicitly illustrated) made of an elastic material such as i O"rubber. A conveyor belt 7 which is only fragmentarily shown and on which the substrata 8 to be printed are deposited extends next to the second transfer cylinder 2.

As shown in Fig. 2 two axial bearer rings 9, 10 made of case-hardened 20 steel are flange-mounted at the ends of each transfer cylinder 1, 2, the respective diameter of each of said bearer rings being essentially identical to the diameter of the corresponding transfer cylinder 1, 2. The exact diameter of the transfer cylinder 1, 2 and of the bearer ring 9, 10 is selected in accordance with the properties of the material so that a defined contact force is maintained between the bearer rings 9 and 10, whereas the transfer cylinders 1, 2 are pressed against each other with an essentially smaller force, as will be explained thereinafter.

The transfer cylinders 1, 2 represented in Figs. 1 and 2 have the same diameter; however, they may also have different diameters. For example, the transfer cylinder 1 and the bearer rings 9 may have a greater diameter than the transfer cylinder 2 and the bearer rings 10. The exact diameter ratio of the bearer rings 9, 10 is adapted to the specific rolling-off conditions of the transfer cylinders 1, 2, as will be described thereinafter.

-6- When in operation the conveyor belt 7 conveys the substrata 8 linearly as indicated by the direction of the arrow, with said substrata 8 being pressed along a linear contact location against the second transfer cylinder 2. The motor 6 causes the second transfer cylinder 2 to rotate so that its circumferential speed corresponds to the conveying speed of the conveyor belt 7. The second transfer cylinder 2 entrains the first transfer cylinder I via bearer rings 9, 10 so that the transfer cylinders 1, 2 roll off against each other as indicated by the direction of the arrows. The imaging head 3 images a latent image on the passing rotating first transfer cylinder 1, said latent image being developed in the inking unit 4. The developed printing image is transferred onto the second transfer cylinder 2 from where it is transferred onto a substratum 8. If necessary, cleaning devices wiping off the ink residues which have not been transferred may be provided at the transfer cylinders 1, 2.

The bearer rings 9, 10 effect a very accurate synchronization of the rotary 15 motion of the transfer cylinders 1, 2. On the path from the imaging head 3 to the transfer location on the second transfer cylinder 2 there may be a slip between the first transfer cylinder and the second transfer cylinder 2, said slip being only a few micrometers or even less, which is tolerable without any causing any problems.

20 A prerequisite however being the fact that the static friction resistance between the bearer rings 9, 10 is greater than that between the transfer cylinders 1, 2. In this case the bearer rings 9, 10 roll off against each other in an almost 3. ideal manner, causing only a very small slip. The fact that, in practice, an inevitable relative motion occurs between the surfaces of the transfer cylinders 1, 2 does not have any effects. The sliding friction resistance of such a relative movement is always smaller than the static friction resistance. Moreover, such relative movements are kept as small as possible from the very beginning by selecting a diameter ratio of the bearer rings 9, 10 which equals the circumferential ratio of the transfer cylinders 1, 2 by taking into account the length of the outer cylindrical rubber surface of the second transfer cylinder 2 when being in operation. This length is caused by a deformation of the outer cylindrical rubber surface of the second transfer cylinder 2 in the area of the transfer location of the first transfer cylinder 1.

-7- Now the contact forces between the bearer rings 9 and 10 are estimated, said contact forces are necessary for the second transfer cylinder 2 to entrain the first transfer cylinder I largely in synchronism.

On the basis of the aforementioned facts the two transfer cylinders 1, 2 are pressed against each other with a force F, required for the transfer process.

Between the transfer cylinders 1, 2 there is a material-dependent static friction coefficient gz. The corresponding static friction resistance is R, Pz Fz. When being at the maximum, said static friction resistance Rz has to be overcome by a static friction resistance RS existing between the bearer rings 9 and 10 which is equal to the product of a contact force F, existing between the bearer rings 9 and and a corresponding material-dependent static friction coefficient ls. Thus, RS P's Fs Ptz F, Rz.

If one of the transfer cylinders is made of steel and the other features an outer cylindrical surface made of rubber, whereas the bearer rings are made of steel, Lz is approximately five times as great as ts- Thus, the contact force F.

between the bearer rings must be at least five times as great as the contact force SFz between the transfer cylinders, ensuring that the friction between the bearer rings prevails and that, with the exception of a slight slip, there is no relative 20 movement therebetween.

In particular in the case of a transfer cylinder and having an outer cylindrical surface made of rubber and being in operation the friction resistance 9°*o may, however, be subjected to temporary fluctuations caused, for example, by ununiform properties of the material or the aforementioned jam of the material in front of the transfer location. For this reason the contact force Fs between the bearer rings is, in practice, essentially greater that the result of the calculations, i.e. it is ten or even twenty times the force Fz with which the transfer cylinders are pressed against each other. Cylinder bearings being able to absorb said forces may be carried out with justifiable efforts, in particular as the ink transfer technologies which are available for digital printing machines often require proportionally small contact forces. Moreover, digital printing machines provide transfer technologies requiring contact forces which are practically of no -8importance and due to which the invention may thus be put into practice very easily.

In the case of an alternative not illustrated in the drawing according to which the first transfer cylinder 1 and not the second transfer cylinder 2 is driven by a motor the torque required at the location at which printing ink is transferred onto the substratum 8 has to be taken into account in addition to the estimated contact forces. The same is true for cases in which not only the transfer cylinder but also further transfer cylinders are to be driven via bearer rings. The drives of the transfer cylinders may be connected in line one after the other, or the bearer rings of a transfer cylinder may drive several transfer cylinders, with additional bearer rings being connected, if necessary, in order to bridge distances between the transfer cylinders. Such a case is shown in Fig. 3.

o The printing machine shown in Fig. 3 comprises three transfer cylinders 11, 12, 13 which are disposed one behind the other above a conveyor belt 14 15 conveying substrata 15 in the direction of the arrow. A motor 16 is connected to the middle transfer cylinder 12 possibly via a gearing (not illustrated), and said motor rotates said middle transfer cylinder in the direction indicated by the arrow.

According to the specimen embodiment of Figs. 1 and 2, the transfer cylinders 11, 12, 13 feature lateral bearer rings which by means of two additional bearer 20 rings 17 are pressed against each other in one row.

When the motor 16 rotates, the bearer rings of the transfer cylinders 11, 12, 13 and the additional bearer rings 17 rotate in the directions indicated by the arrows, and the transfer cylinders 11, 12, 13 rotate by passing the imaging heads 18 and inking units (not illustrated) in order to transfer the printing images onto the substrata The principle shown in Fig. 3 may be versatily modified and extended. It is conceivable to drive, for example, four or five printing units instead of just three.

Furthermore, each of said printing units may feature not only one transfer cylinder 11, 12, or 13, as shown in Fig. 3, but rather a system comprising two transfer cylinders, as shown in Figs. 1 and 2, or even more transfer cylinders. Even with such a chain of transfer cylinders connected to each other via bearer rings, the slip between the bearer rings which has added up remains tolerable, as its -9magnitude is still within the range of micrometers, and thus it does not perceptibly affect the register of the printing images.

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Claims

1. A device for driving a plurality of transfer cylinders of a digital printing machine, comprising a motor to which one of the plurality of transfer cylinders is connected, and bearer rings rollable on one another under a preloading, the plurality of transfer cylinders being connected to one another via said bearer rings, and said transfer cylinders which are not connected to the motor being substantially exclusively driven through said respective bearer ring.

2. The device according to claim 1, wherein one of said bearer rings is axially fastened to each axial end of each transfer cylinder of said plurality of transfer cylinders; at least, respectively, two of said plurality of transfer cylinders and the bearer rings corresponding thereto being rollable on one another; the preloading between the bearer rings of two transfer cylinders rolling on one another multiplied by a static friction coefficient of the contacting surfaces of said bearer rings is greater than a contact force (Fz) existing between the two transfer cylinders multiplied by a static friction coefficient of the contacting surfaces of the two transfer cylinders. 20

3. The device according to claim 2, wherein a ratio of the diameters of said o. bearer rings of the two transfer cylinders rollable on one another is substantially equal to a ratio of the transfer cylinder circumferences effective during oo ".operation. 25

4. A device according to claim 2 or claim 3, including one transfer cylinder of two transfer cylinders rolling off against each other features an outer cylindrical surface made of an elastic material for transferring printing ink onto a substratum. S

5. A device according to claim 4, including a motor connected to the transfer cylinder featuring an outer cylindrical surface made of an elastic material. vds\ndelete74125-96.doc 11

6. The device according to any preceding claim, including further bearer rings connecting respective transfer cylinders of a plurality of printing units of the printing machine to one another, said motor being connected to one of the transfer cylinders of the plurality of printing units. DATED: 2 May, 2000 PHILLIPS ORMONDE FITZPATRICK Attorneys for: HEIDELBERGER DRUCKMASCHINEN AKTIENGESELLSCHAFT 4* a- a.. t a ***ft ftf ft ft g* W:\chrs\nodelete\74125-96.doc